v1.2.0: Add 4 new protocols, fix 5 existing, port Kia V6 encoder

New protocols (from ProtoPirate):
- Mazda V0: 433MHz, pair-based decoding, XOR deobfuscation
- Mitsubishi V0: 868MHz, PWM, bit negation + XOR unscrambling
- Porsche Touareg: 433/868MHz, sync preamble, 24-bit rotate cipher
- Fiat V1 (Magneti Marelli BSI): 433MHz, auto-detected timing variants

Protocol fixes aligned with ProtoPirate reference:
- Kia V1: Fix Manchester level mapping (inverted convention), off-by-one
  bit count, CRC4 simplified to 7 bytes + offset 1
- Kia V2: Fix CRC byte layout (was double-counting nibbles), off-by-one
  bit count, preamble short-HIGH handling
- Fiat V0: Fix endbyte transform (remove (<<1)|1), standard Manchester
  encoder (was differential), 7 btn bits (was 6), gap path fallback
- PSA: Fix modified TEA (XTEA-like dynamic key selection), XOR decrypt
  byte mapping, critical key2_low construction bug, encoder polarity and
  preamble, add key1_high nibble validation, dual preamble patterns
- Ford V0: Add calculate_checksum (sums all serial+count bytes) for encoder

Kia V6 encoder ported:
- Forward AES-128 (SubBytes, ShiftRows, MixColumns, encrypt)
- encrypt_payload: build plaintext, AES encrypt, pack into 3 parts
- Two-pass Manchester upload (640 + 38 preamble pairs)
- fx_field extraction stored in DecodedSignal.extra for encode roundtrip

Updated README, protocol docs, and version bump to 1.2.0.

docs/mitsubishi_v0.md

@@ -0,0 +1,59 @@
+---
+layout: default
+---
+
+# Mitsubishi V0 Protocol
+
+**Rust module:** `src/protocols/mitsubishi_v0.rs`
+**Reference:** `REFERENCES/ProtoPirate/protocols/mitsubishi_v0.c`
+
+## Overview
+
+Mitsubishi V0 uses PWM encoding at 250/500 us. 96-bit frame (12 bytes). Level-aware: HIGH pulses are saved, LOW pulses complete the pair. After collection, data is unscrambled via bitwise NOT + counter-derived XOR mask.
+
+## Timing
+
+| Parameter | Value  | Notes        |
+|-----------|--------|--------------|
+| Short     | 250 us | +/-100 us    |
+| Long      | 500 us | +/-100 us    |
+| Min bits  | 80     |              |
+| Frame     | 96 bits| 12 bytes     |
+
+## PWM Bit Encoding
+
+| Pair (HIGH, LOW) | Bit |
+|------------------|-----|
+| Short HIGH + Long LOW  | 1 |
+| Long HIGH + Short LOW  | 0 |
+
+Bits collected MSB-first into a 12-byte buffer.
+
+## Frame Layout (96 bits)
+
+After unscrambling:
+- Bytes 0-3: Serial (32 bits, big-endian)
+- Bytes 4-5: Counter (16 bits)
+- Byte 6: Button (8 bits)
+- Bytes 7-11: Remaining payload
+
+## Unscramble Algorithm
+
+1. Bitwise NOT the first 8 bytes.
+2. Extract counter from bytes [4..5]: `hi = (counter >> 8) & 0xFF`, `lo = counter & 0xFF`.
+3. Compute masks: `mask1 = (hi & 0xAA) | (lo & 0x55)`, `mask2 = (lo & 0xAA) | (hi & 0x55)`, `mask3 = mask1 ^ mask2`.
+4. XOR bytes [0..5] with mask3.
+
+## Decoder Steps
+
+1. **Reset** -- Wait for HIGH pulse; save duration.
+2. **DataSave** -- On HIGH: save duration. On LOW (unexpected): reset.
+3. **DataCheck** -- On LOW: decode pair. If 96 bits collected, unscramble and return. Otherwise continue.
+
+## Encoder
+
+Not supported (decode-only).
+
+## Frequencies
+
+868.35 MHz.